1. Field of the Invention
The present invention relates to an antenna.
2. Description of the Prior Art
GSM mobile phone services have been allocated three bands. In most countries 900 MHz (880-960 MHz) and 1880 MHz (1710-1880 MHz) bands are used. However, in the United States, GSM services have been allocated a 1900 MHz (1850-1990 MHz) band. A broadband antenna is desirable so that mobile phones that can operated in both the 1800 MHz and 1900 MHz bands, which overlap. However, conventional broadband antennas are too large to be incorporated into the small form of modern mobile phones.
One solution to this problem, that has been tried, is the use of two elements both tuned to the middle of the combined 1800 MHz/1900 MHz band. This has to effect of producing a wider, double peak or flat-top frequency characteristic.
According to the present invention, there is provided an antenna comprising a driven element, resonant at a first frequency and a parasitic element, wherein the parasitic element is resonant at a second different frequency and the resonant frequencies are such that the antenna has an operational band of usable frequencies encompassing the first and second frequencies.
It has been found that improvements in return loss, over the prior art where both elements resonate at the same frequency, can be achieved.
Preferably, both of the elements are connected to ground at one end.
A further parasitic element may be included which is resonant at a third frequency, substantially lower than the first and second frequencies, and has an operational band that does not overlap that of the combination of the first and second elements. The further parasitic element may meander and be connected to ground at one end.
Preferably, the elements comprise foil patterns of a substantially planar substrate. The driven element and the further parasitic element preferably comprises foil patterns on a major face of the substrate and the other parasitic element comprising a foil pattern along an edge of the substrate. More preferably, a common ground terminal for connecting the elements to an external ground and a single feed terminal for connection to an external signal feed. The terminals may be located at the floor of a peripherally located stepped portion of the substrate.
According to the present invention, there is also provided an antenna comprising a substantially planar substrate, a first driven element, resonant at a first frequency, a second driven element, resonant at a second, lower frequency, a parasitic element associated with the first driven element, a common ground terminal for connecting all of the elements to an external ground and a single feed terminal for connection to an external signal feed, wherein the elements and terminals comprise a conductive pattern on the substrate.
The second driven element may meander.
Preferably, the driven elements comprise foil patterns on a major face of the substrate and the parasitic element comprises a foil pattern along an edge of the substrate.
Preferably, the substrate includes a peripherally located stepped portion and the terminals are located at the floor of the stepped portion.
An antenna according to the present invention may be mounted within the casing of a mobile phone.